1. Introduction
Plant cells, like whole plants, require a balanced diet of minerals to grow and develop. Unlike soil-grown plants that extract nutrients from the earth and water, tissue cultures rely entirely on what’s provided in the media.
Nutrient deficiencies, toxicities, or imbalances can lead to poor callus growth, failed shoot regeneration, or abnormal tissue morphology.
2. Macronutrients – The Major Nutrients
These nutrients are needed in concentrations ranging from hundreds to thousands of milligrams per liter.
| Macronutrient | Function |
|---|---|
| Nitrogen (N) | Vital for protein, enzyme, and DNA synthesis. MS contains both ammonium (NH₄⁺) and nitrate (NO₃⁻) for balance. |
| Phosphorus (P) | Important for ATP, cell division, and root growth. |
| Potassium (K) | Regulates enzyme activity, osmotic balance, and stomatal function. |
| Calcium (Ca) | Stabilizes cell walls and membranes, key for root and shoot development. |
| Magnesium (Mg) | The central atom in chlorophyll and enzyme cofactor. |
| Sulfur (S) | Used in amino acids and defense compounds. |
📌 Macronutrients in MS Medium
3. Micronutrients – The Trace Heroes
Micronutrients are needed in micrograms to milligrams per liter, but they’re no less important.
| Micronutrient | Function |
|---|---|
| Iron (Fe) | Essential for chlorophyll synthesis and electron transport; added as Fe-EDTA to remain soluble. |
| Manganese (Mn) | Involved in photosynthesis and cell wall structure. |
| Zinc (Zn) | Aids in enzyme activity and auxin synthesis. |
| Copper (Cu) | Plays a role in redox reactions and lignin formation. |
| Boron (B) | Required for cell wall strength and division. |
| Molybdenum (Mo) | Needed for nitrate reduction in nitrogen metabolism. |
Too much of a micronutrient can become toxic, especially in long-term cultures.
4. Nutrient Interactions and Adjustments
Even in sterile media, nutrients can interfere with one another:
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Ammonium toxicity can occur if NH₄⁺ is too high and not balanced with NO₃⁻.
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Iron precipitates at high pH unless chelated with EDTA.
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Excess potassium can reduce calcium uptake.
Signs of imbalance:
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Yellowing tips = nitrogen or iron deficiency
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Darkened roots = phosphate toxicity
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Twisted leaves = boron toxicity
5. Customizing Nutrient Formulations
MS works well for many herbaceous plants, but some species—especially woody, slow-growing, or exotic types—need fine-tuned media.
Examples:
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WPM (Woody Plant Medium) → Less nitrogen, better for trees
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Modified MS → Altering ammonium/nitrate ratio
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Orchid media → Low nitrogen, added amino acids
Always consider plant species, age, and propagation goal before finalizing media composition.